Recently, the technology of forming an optical device using a semiconductor platform has been developed. For example, a silicon platform optical device of a silicon material has been studied and developed.
In the field of a semiconductor device, an advanced and inexpensive micromachining technology has been realized. By applying this technology to optical components, an inexpensive and small optical device (for example, an optical transmitter, an optical modulator) may be produced. Therefore, a semiconductor platform optical device is considered as an important device in the optical communication over an optical network, an optical interconnection, etc.
FIG. 1 illustrates an example of an optical modulator formed on a semiconductor platform. This optical modulator is an all-pass ring resonator optical modulator, and includes a bus waveguide 101, a ring resonator 102, and an electrode 103. The bus waveguide 101 and the ring resonator 102 are optical waveguides formed on a semiconductor platform. The bus waveguide 101 and the ring resonator 102 are optically coupled to each other. The ring resonator 102 is formed between a pair of electrodes 103, as illustrated in FIG. 1.
In the optical modulator with the above-mentioned configuration, continuous wave light of a specified wavelength is input to the bus waveguide 101. A portion of the continuous wave light is guided to the ring resonator 102. The continuous wave light guided to the ring resonator 102 is propagated counterclockwise, and then output to the bus waveguide 101 in the example illustrated in FIG. 1. The perimeter of the ring resonator 102 is determined to have a specified relationship with the wavelength of the continuous wave light. A data signal is applied to the electrode 103. By so doing, the optical path length of the ring resonator 102 is changed depending on the data signal. Therefore, the optical modulator can generate a modulated optical signal which carries the data signal.
Since the optical modulator with the above-mentioned configuration uses a resonance effect, the power consumption is low. In addition, it is easy to downsize this optical modulator, for example, 10 μm×10 μm in size. However, it is necessary that the operating wavelength which depends on the perimeter of the ring resonator 102 matches the wavelength of incoming light with very high accuracy.
Furthermore proposed is an optical transmitter having a plurality of ring modulator (For example, Xuezhe Zheng et. al., Ultra-Low Power Arrayed CMOS Silicon Photonic Transceivers for an 80 Gbps WDM Optical Link, National Fiber Optic Engineers Conference, Optical Society of America, 2011, PDPA1). In the optical transmitter, each ring modulator is realized by, for example, the optical modulator illustrated in FIG. 1. The plurality of ring modulators are optically coupled to a common bus waveguide. According to the configuration, a wavelength division multiplexing optical transmitter is realized. However, in the configuration, it is necessary that the wavelength of each channel of input light matches corresponding operating wavelength of each ring modulator with high accuracy. Therefore, in the optical transmitter, the control for obtaining an appropriate operation state is complicated. If the operating wavelength of the ring modulator is inappropriately adjusted in the above-mentioned optical transmitter, then, for example, a data signal to be transmitted using a certain wavelength channel may be assigned to another wavelength channel.
Further proposed is an optical integrated device (for example, Japanese Laid-open Patent Publication No. 2010-27664) including a semiconductor laser and an optical modulator (resonator-based optical modulator) coupled to the semiconductor laser. This optical integrated device includes a waveguide wavelength filter for extracting only the light (modulated light) in an oscillation mode included in the resonant wavelength band of the optical modulator. The wavelength filter is a ring resonator-based wavelength filter. However, in the configuration, it is necessary to perform complicated control to match the operating wavelength of the ring resonator which realizes an optical modulator and the operating wavelength of the ring resonator which realizes a wavelength filter with the signal wavelength.
The technology of forming an optical device on a semiconductor platform is also described in, for example, Po Dong et. al., Low Vpp, ultralow-energy, compact, high-speed silicon electro-optic modulator, Opt. Express, OSA, 2009 Vol. 17, No. 25, 22484-22490.
As described above, in the related art, the control for correctly operating an optical transmitter or an optical modulator having a ring resonator is complicated.